Flavonoid glycosides hydrolysis

Identification of flavonoids Quantification of individual flavonoids depends heavily on the availability of standard references. Only a limited number of common flavonoids are commercially available as standards. Standard references for flavonoid glycosides are particularly difficult to find thus direct quantification of the native glycosides is nearly impossible. Analysis of the aglycones after acid or enzymatic hydrolysis is therefore common practice. When standard flavonoids are not available, or when unknown compounds are encountered in a particular fruit or vegetable, use of a DAD... 

Flavonoid aglycones (isolated by acid hydrolysis of the corresponding flavonoid glycosides)... 

Bokkenheuser, V.D., Shackleton, C.H., and Winter, J., Hydrolysis of dietary flavonoid glycosides by strains of intestinal Bacteroides from humans, Biochem. J., 248, 953, 1987. 

Alaniya MD, Kinetics of the alkaline hydrolysis of flavonoid glycosides. Chem Nat... 

Flavonoid glycosides after intake by the insects are also sequestrated without hydrolysis and can be found in the insect tissues. 

Another quantitative RP HPLC method, based on the reduction of the complex flavonoid glycoside pattern by acid hydrolysis to one major aglycone (quercetin) and one C-glycoside (vitexin), was developed and employed for the characterization of Crataegus leaves and flowers. 

Harborne compared the behavior of flavonoid glycosides and of several C-glycosyl compounds in a 1 1 solution of ethanol in 2 V hydrochloric acid at 100°, and found that the former are invariably hydrolyzed, whereas the latter are not. Thus, even apigenin 7-D-glucosiduronic acid, which is resistant to acid hydrolysis, is completely cleaved in 4 hours, whereas no C-glycosyl compound tested liberates sugar under these conditions. This procedure provides a convenient method for distinguishing between the two types of compound. 

Flavonoids can be considered as important constituents of the human diet—average consumption is estimated at approximately 1 g flavonoids per person per day, although the amount of absorbed flavonoids may be much lower. Flavonoid glycosides are poorly absorbed until undergoing hydrolysis by bacterial enzymes in the intestine, whereupon their aglycones can be absorbed. However, recent studies suggest a fair level of absorption of flavonol glycosides from the small intestine can also occur (Gee and Johnson 2001). 

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